1. Field of the Invention
The present invention relates to a scheme for adjusting output impedance, and more particularly to a driving apparatus, driving circuit, and corresponding methods for using current adjustment to adjust the output impedance so as to make the output impedance match with the impedance of a transmission line.
2. Description of the Prior Art
Generally speaking, the output impedance of a line driver connected to a transmission line is usually designed to be matched with the characteristic impedance of the transmission line, to minimize signal reflection and avoid attenuated efficiency of signal transmission. A conventional line driver used with a transmission line may adjust resistances of its multiple resistors to adjust the amplitude of its output signal and output impedance to try to make its output impedance be equal to the impedance value specified by the standard of the transmission line, so as to make its output impedance match with the characteristic impedance of the transmission line. The conventional line driver is configured to compare the actual amplitude of the output voltage with that of a reference voltage and to control the resistances of the above-mentioned resistors based on the voltage comparison result, for adjusting its output impedance. However, practically, since it is necessary for the conventional line driver to employ the multiple resistors to adjust its output impedance by using voltage adjustment, the circuit size of conventional line driver would inevitably become larger, and the circuit cost would be increased unfortunately. Thus, in order to decrease the circuit cost, it is important to develop another scheme for adjusting the output impedance.